1. Field of Invention
The present invention relates to a process for the preparation of cyclopropanecarboxamide by reaction of cyclopropanecarboxylic esters with NH.sub.3 in the presence of catalytic amounts of an alcoholate and in the absence of a hydrocarbon solvent.
Cyclopropanecarboxamide is an organic intermediate which, for example after conversion to cyclopropylamine, is reacted to give active compounds in the pharmaceutical and plant protection sector. Such a use requires that all intermediates be prepared in high purities, which have not been achieved in previous preparative processes, so that additional, yield-reducing purification steps had to be carried out subsequently.
2. Description of the Related Art
The reaction of esters with ammonia to give the corresponding amides is generally known; in the known cases, a solvent or solvent mixture is always used.
Thus, according to DE-OS (German Published Specification) 1,939,759 (equivalent to U.S. Pat. No. 3,711,549), a mixture of 0.15 mol of sodium methoxide and 0.95 mol of methyl cyclopropanecarboxylate is reacted in 40 ml of methanol and 390 ml of toluene with ammonia at about 80.degree. C. This gives a conversion of 85-90%; however, this result is only achieved, if the preferred methanol concentration of 40-80 ml/mol of the ester, which in turn is used in a 20-25% strength solution in toluene, is maintained. If the toluene is left out, lower yields of amide are obtained. Likewise, the degree of conversion drops to about 59%, if methanol is left out. In a variation of the procedure on a large industrial scale, the operating pressure reaches 28 atm. The conversion rate of 90%, which is the optimum obtainable under these conditions, makes a workup by distillation necessary, in which methanol, toluene and unconverted methyl cyclopropanecarboxylate have to be recycled. Water and hydrochloric acid are then added to the flask residue which is obtained in such a distillation and consists of cyclopropanecarboxamide, remaining toluene and sodium methoxide, since the amide is susceptible to hydrolysis in an alkaline, aqueous medium; the aqueous phase is separated off in a separatory funnel, and the organic phase is again extracted with water. The cyclopropanecarboxamide is then present in the highly dilute aqueous solution thus obtained.
EP 205,403 describes the reaction of sterically hindered secondary and tertiary cyclopropanecarboxylic esters with ammonia, using a different catalyst, namely the sodium salt of polyhydric alcohols, such as glycol or glycerol In this reaction, excess polyhydric alcohol has to be used to maintain a homogeneous catalyst solution. The catalyst can also be dissolved by using methanol. A further solvent used is xylene. In the workup, the polyhydric alcohol then needs to be removed azeotropically, which, in the case of glycol, is achieved, for example, by means of p-cymene, after which water is added and the p-cymene is removed azeotropically. The EP application mentioned reports operating temperatures of 100-200.degree. C., operating pressures of up to 16 bar and yields in the range from 50-91%.